The present invention relates generally to rotary machines, and more particularly to actuated seals for rotary machines such as steam and gas turbines.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, a gas path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
It is known in the art of steam turbines to position, singly or in combination, variable clearance labyrinth seal carrier segments and brush seals in a circumferential array between the rotor of the turbine and the circumferentially surrounding turbine casing to minimize steam-path leakage. The ends of coil springs engage circumferentially-opposing and generally-matching holes in circumferentially-adjacent seal segments. The coil springs circumferentially urge apart the circumferentially-adjacent seal segments. In addition, such circumferentially-urging-apart causes the seal segments to move radially outward within a channel in the casing. This prevents damage to the labyrinth-seal teeth from transient radial movement of the rotor during turbine startup. While the coil springs have proved to be quite reliable, performance of the coil springs and the radially inward movement of the circumferentially-adjacent seal segments is dependent on the internal pressure of the turbine which at times is an non-uniform pressure on the seal segments thereby opening the seal clearance between the turbine casing and the rotor.
Accordingly, there is a need in the art for a rotary machine having improved leakage control between stationary and rotating components.
One embodiment of the present invention comprises a seal assembly for a rotary machine wherein the rotary machine comprises a rotor and a casing. The rotor comprises a generally longitudinally-extending axis wherein the casing is generally coaxially aligned with the axis. The casing circumferentially surrounds and is radially spaced apart from the rotor wherein the casing comprises an inner circumferential channel generally coaxially aligned with the rotor. The seal assembly comprises a plurality of seal segments disposable in a circumferential array in the channel so as to be movable between radially inward and radially outward positions. In addition, the seal assembly comprises a plurality of displacement apparatuses comprising at least one fluid inlet and configured for urging apart the seal segments upon introduction of a fluid medium in the fluid inlet. Each of the seal segments comprises an end having at least one of the displacement apparatuses circumferentially disposed thereon.